Lumbar spinal stenosis is a condition in which the nerves in the spinal canal become compressed. Patients with spinal stenosis can suffer from pain in the lower back and legs. The pain is classically worse when patients walk, and better when they stop walking and flex forward. This is because flexion tends to open up the spinal canal.
As an alternative to traditional laminectomy, there is a small titanium implant device available known as “x-stop” which may be placed between the posterior spinous processes of the affected levels (usually L3/4 or L4/5). Implanting the x-stop device effectively produces a permanent slight flexion, which in turn can provide symptom relief and improve physical function. The x-stop may be implanted with minimally invasive surgery; there is usually no removal of tissue or bone; and the procedure is reversible if necessary.
In one known procedure, the patient is positioned in the lateral decubitus position (right side down) and anesthetized locally. A 4-8 cm midline incision is made to expose the fascia, and the surgeon then incises the fascia on either side of the spinous processes and the supraspinous ligament. A dilator and, in turn, a sizer may then be used to open up the interspinous ligament. At this point, the patient is ready for the x-stop implant.
Referring to FIGS. 1-3, a known instrument 10 for implanting the x-stop device includes a handle 11, a shaft 12, and a securement mechanism 14. The securement mechanism is mechanically coupled to a finger-operated slider 16. When the slider 16 is retracted, an axially extending rod 14a is retracted, and a pair of pins (one of which, 14b, is shown in FIG. 1) may be inserted into a pair of holes (14c, see FIG. 3) in the wings of the main portion of an x-stop device 20. When the surgeon releases the slider 16, the rod 14a moves forward into another hole 14d in the main body 21 of the x-stop device (see FIG. 3), which hole 14d is oriented at 90 degrees relative to the holes 14c, so that the securement mechanism 14 locks firmly into engagement with the x-stop device 20. The above device is described, inter alia, in U.S. Pat. No. 7,510,567, the relevant portions of which are incorporated herein by reference.
Referring to FIG. 3, the x-stop device comprises a head 21, a pair of wings 22 extending in opposite directions from the head 21, a cylindrical spacer element 24 (whose diameter may vary depending on the patient), and a wedge portion 26 with a leading edge 27.
Referring to FIGS. 2-3, when the x-stop is to be implanted, it is moved so that the leading edge 27 of the wedge portion 26 positioned between, the pair of spinous processes 28a, 28b of the affected levels. The surgeon maneuvers the handle 11 so that the wedge portion 26 moves in the direction of arrow 18 between the spinous processes 28a, 28b. Thereafter, as shown in FIG. 3, after the wedge portion 28 has passed between the spinous processes, the wings 22 position the x-stop so that the spacer element 24 is positioned between the spinous processes 28a, 28b. At this point, the surgeon again retracts the slider 16, which retracts the extending rod 14a to allow the pins 14b of the insertion instrument to be withdrawn from the holes 14c and thus allows the instrument to release the x-stop device inside the patient and withdraw the instrument.
Finally, a second wing element (not shown, but which is similar to the portions 21-22 of the main x-stop device), is inserted into the patient and secured to on the wedge portion 26, using hole 30, so that the spacer is secured on both sides of the spinous processes 28a, 28b. 